[poky] build performance: bb-matrix on 4-core (BB_NUMBER_THREADS and PARALLEL_MAKE optimization)

[Richard Purdie]

On Wed, 2011-07-06 at 11:16 -0700, Darren Hart wrote:
> I ran the attached bb-matrix.sh on the following system:
> 
> CPU (1): Intel(R) Core(TM) i7 CPU         870  @ 2.93GHz
> Cores: 4
> Threads: 8
> Memory: 8186560 kB
> OS Disk: INTEL SSDSA2M040G2GC (SSD)
> Build Disk: Hitachi HDT721050SLA360 (Spinning Media)
> 
> The script runs builds with all combinations of BB_NUMBER_THREADS and
> PARALLEL_MAKE from 4 through 16.
> 
> Once BB_NUMBER_THREADS hit 10, the kernel OOM Killer started killing off
> tasks and build time tripled. Those runs have been removed the dataset.
> 
> All of the runs with PARALLEL_MAKE=10 also failed, for a variety of
> reasons. See bb-pm-errors.txt for details. For whatever reason, 10 seems
> to be a bad number. Additional failures were seen at 09-11 and 10-14.
> These have all been removed from the dat file.
> 
> From the remaining results, a clear downward trend in build time is
> evident with increasing BB_NUMBER_THREADS through 8, while build time
> mostly increases again with 9 (and dramatically so with 10, not shown).
> Optimal build time is achieved with BB_NUMBER_THREADS=8.
> 
> Along the BB_NUMBER_THREADS=8 line, there is no clear trend with
> increasing values of PARALLEL_MAKE. Local downward trends appear from
> 4-7 and from 11-14. Optimal build time occurs with PARALLEL_MAKE=14,
> however, it only bests PARALLEL_MAKE=7 by 68 seconds.
> 
> While optimal build time is achieved with BB=8 and PM=14, a more
> resource friendly setting of BB=8 and PM=6 yields nearly as good results.

Thanks Darren, I think those are interesting results.

Is the general advice we should give out therefore to set
BB_NUMBER_THREADS = PARALLEL_MAKE = number threads?

I'd love to understand why there is the peak and second dip on the
PARALLEL_MAKE curve...

It would also be good to put the script in scripts/contrib.

Cheers,

Richard